The present invention is directed to apparatus for controlling the intermittent operation of a low production (less than 50 barrels a day) well. More particularly, the present invention is directed to apparatus for operating the pump on a secondary recovery well intermittently responsive to the well tubing pressure (i.e., to a pressure activated, pump-off control).
Many "vintage" oil wells are of low capacity or production, that is, less than 50 barrels of oil per day. These wells are typically being produced using secondary recovery methods (i.e., they are being produced using artificial lift techniques, pumps) and, in some cases, tertiary recovery methods (i.e., in addition to pumping, gas, steam, water, or chemicals are injected to enhance the amount of oil produced from a given pore volume).
Due to the low production rates of these wells, continuous pump operation may not be possible, even by slowing the pump to its slowest operating speed. Conventional intermitting devices comprise time clocks that will operate a well for, say, 20 minutes every two hours. Such clocks are not entirely satisfactory. While the pumping system is designed to operate with a minimum of supervision, these intermitting clocks must be monitored fairly closely and, as the production of the well is steadily reduced, the clocks need readjustment. Improper adjustment of the time clock can not only result in inefficient operation (e.g., failure to produce all fluid available for under-pumping, wasted energy for over-pumping), it can increase wear and tear on the equipment (due to "pounding fluid") leading to premature failure of one or more components of the system. In the present uncertain market, the added expense associated with a well workover can be a key factor in determining to shut in a low producing well.
The present invention overcomes these difficulties resulting in more efficient, cost-effective operation of the pump. A pressure sensor, in conjunction with a series of three timers, control the operation of the pump. A first timer (one of two timing devices on a dual adjustable timer), known alternatively as the "fill-in" timer and the "off" timer of the repeatable timer T.sub.R, disables the operation of the pump for a first period of time during which well fluids accumulate in the tubing (i.e., the well "fills in").
When the fill-in timer "times out" (its set time period elapses), circuit means turn on the pump motor for a second period of time of a duration partly determined by a second timing device on the dual adjustable timer, known alternatively as the "pump-up" timer or the "on" timer of the repeatable timer, T.sub.R.
The period of operation of the pump motor is only partially determined by the pump-up timer because if the pressure sensor determines that a particular minimum tubing pressure desired for production is present, then circuit means will switch control of the pump motor from the pump-up timer to the combined control of yet a third timer in conjunction with said pressure sensor, this third timer being known alternatively as the "pump-off" timer or the delay timer T.sub.D. If "pressure is made" (minimum tubing pressure achieved), a normally closed pressure switch will be opened on each stroke of the pump in which this minimum pressure is present. Opening of this switch interrupts power to the pump-off timer causing it to be reset (i.e., to start its timing cycle over). As soon as pressure is not made, the pump-off timer times out shutting off the pump motor after a third period of time (selected to correspond with the particular number of pump strokes necessary to achieve a fully pumped-off condition) and circuit means restores control to the fill-in timer for another cycle. Should pressure not be met within the second time period, the pump-up timer times out and the circuit means restores control to the fill-in timer again, initiating another cycle. The present pressure-activated pump-off control improves pump efficiency, reducing non-productive pump operation, and lifting all fluid that has accumulated. Wear on the mechanical components associated with fluid pounding is reduced as is the possibility of gas locks.
Various other features, characteristics, and advantages of the present invention will become apparent after a reading of the following specification.